Fumed silica
Fumed silica, also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler.Properties
Fumed silica has a very strong thickening effect. Primary particle size is 5–50 nm. The particles are non-porous and have a surface area of 50–600 m2/g. The density is 160–190 kg/m3.Production
Fumed silica is made from flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a electric arc. Major global producers are Evonik, Cabot Corporation, Wacker Chemie, Dow Corning, Heraeus, Tokuyama Corporation, OCI, and .Applications
Fumed silica serves as a universal thickening agent and an anticaking agent in powders. Like silica gel, it serves as a desiccant. It is used in cosmetics for its light-diffusing properties. It is used as a light abrasive, in products like toothpaste. Other uses include filler in silicone elastomer and viscosity adjustment in paints, coatings, printing inks, adhesives and unsaturated polyester resins. Fumed silica readily forms a network structure within bitumen and enhances its elasticity.Health issues
While fumed silica is not listed as a carcinogen by OSHA, IARC, or NTP, it can easily become airborne due to its fineness and thinness, making it at the very least an inhalation hazard capable of causing irritation.